Method for allowing terminal to transmit power headroom information in wireless communication system and device therefor

ABSTRACT

A method and a user equipment (UE) are described for transmitting power headroom (PH) information. The UE generates PH information, and transmits the PH information to a base station. The PH information includes a first field including a plurality of indicators, each of the plurality of indicators indicating the presence of a second field indicating a PH level of a corresponding secondary cell (SCell). The PH information further includes a type-1 PH field and a type-2 PH field for a primary cell (PCell). Each of the plurality of indicators is set to 0 or 1. An indicator, which has been set to 1, indicates that the second field exists for the corresponding SCell, and an indicator, which has been set to 0, indicates that the second field does not exist for the corresponding SCell.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of copending U.S. application Ser.No. 13/701,340 filed on Nov. 30, 2012, which is the National Phase ofPCT/KR2011/004440 filed on Jun. 17, 2011, which claims priority under 35U.S.C. 119(e) to U.S. Provisional Application Nos. 61/356,552 filed onJun. 18, 2010 and 61/373,256 filed on Aug. 12, 2010 and under 35 U.S.C.119(a) to Patent Application No. 10-2011-0058045 filed in Republic ofKorea on Jun. 15, 2011. The contents of all of these applications arehereby incorporated by reference as fully set forth herein in theirentirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a wireless communication system, andmore particularly to, a method for allowing a terminal to transmit powerheadroom information in a wireless communication system, and anapparatus for the same.

Discussion of the Related Art

As an example of a mobile communication system to which the presentinvention is applicable, a 3rd Generation Partnership Project Long TermEvolution (hereinafter, “LTE”) communication system is described inbrief.

FIG. 1 is a diagram schematically showing a network structure of anE-UMTS as an exemplary radio communication system. An Evolved UniversalMobile Telecommunications System (E-UMTS) is a system evolving from aconventional Universal Mobile Telecommunications System (UMTS) and basicstandardization task thereof is currently underway in the 3GPP. TheE-UMTS may be generally referred to as a Long Term Evolution (LTE)system. For details of the technical specifications of the UMTS andE-UMTS, reference can be made to Release 7 and Release 8 of “3rdGeneration Partnership Project; Technical Specification Group RadioAccess Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE) 120, eNode Bs (eNBs) 110 a and 110 b, and an Access Gateway (AG) which islocated at an end of the network (E-UTRAN) and connected to an externalnetwork. The eNode Bs may simultaneously transmit multiple data streamsfor a broadcast service, a multicast service, and/or a unicast service.

One or more cells may exist in one eNode B. A cell is set to use one ofbandwidths of 1.25, 2.5, 5, 10, and 20 MHz to provide a downlink oruplink transport service to several UEs. Different cells may be set toprovide different bandwidths. The eNode B controls data transmission andreception for a plurality of UEs. The eNode B transmits downlinkscheduling information with respect to downlink data to notify acorresponding UE of a time/frequency domain in which data is to betransmitted, coding, data size, and Hybrid Automatic Repeat and reQuest(HARD)-related information. In addition, the eNode B transmits uplinkscheduling information with respect to uplink data to a corresponding UEto inform the UE of an available time/frequency domain, coding, datasize, and HARQ-related information. An interface for transmitting usertraffic or control traffic may be used between eNode Bs. A Core Network(CN) may include the AG, a network node for user registration of the UE,and the like. The AG manages mobility of a UE on a Tracking Area (TA)basis, wherein one TA includes a plurality of cells.

Although radio communication technology has been developed up to LTEbased on Wideband Code Division Multiple Access (WCDMA), the demands andexpectations of users and providers continue to increase. In addition,since other radio access technologies continue to be developed, newtechnical evolution is required to secure competitiveness in the future.For example, decrease of cost per bit, increase of service availability,flexible use of a frequency band, simple structure, open interface, andsuitable power consumption by a UE are required.

Recently, 3GPP has been establishing a standard task for a subsequenttechnique of LTE. In this specification, such a technique is referred toas “LTE-Advanced” or “LTE-A”. One of the main differences between an LTEsystem and an LTE-A system is a system bandwidth. The LTE-A system isaimed at supporting a broadband of a maximum of 100 MHz, and to thisend, the LTE-A system is designed to use a carrier aggregation orbandwidth aggregation technique using a plurality of frequency blocks.Carrier aggregation employs a plurality of frequency blocks as one biglogical frequency band in order to use a wider frequency band. Abandwidth of each frequency block may be defined based on a bandwidth ofa system block used in the LTE system. Each frequency block istransmitted using a component carrier.

SUMMARY OF THE INVENTION

An object of the present invention devised to solve the problem lies inproviding a method for allowing a terminal to transmit power headroominformation in a wireless communication system, and an apparatus for thesame.

An object of the present invention can be achieved by providing a methodfor transmitting, by a user equipment (UE) in which at least one servingcell is set, power headroom (PH) information in a wireless communicationsystem, including generating the power headroom information, andtransmitting the power headroom information to a base station.

Alternatively or additionally, the power headroom information includes afirst field including a plurality of indicators and at least one secondfield indicating a level of the power headroom, and each of theplurality of indicators indicates whether the at least one second fieldexists for each of the at least one serving cell.

Alternatively or additionally, each of the plurality of indicators isset to 0 or 1, an indicator, which has been set to 1, indicates that asecond field exists for a corresponding serving cell, and an indicator,which has been set to 0, indicates that a second field does not existfor a corresponding serving cell.

Alternatively or additionally, the at least one second field may be foran activated serving cell among the at least one serving cell.

Alternatively or additionally, in the case in which generation of asecond field corresponding to any one of the at least one serving cellis triggered, the at least one second field may be for the whole of theat least one serving cell.

Alternatively or additionally, the power headroom information may betransmitted through one of the at least one serving cell.

Alternatively or additionally, the first field is a field in a bitmapform, and may be included the power headroom information regardless ofwhether the at least one second field exists.

Alternatively or additionally, the power headroom information may beincluded in a medium access control (MAC) control element (CE).

Alternatively or additionally, the MAC CE may further include a logicalchannel ID (LCID) for notifying existence of the power headroominformation.

Alternatively or additionally, the at least one second field may beconfigured in a cell index order of each of the at least one servingcell.

In another aspect of the present invention, provided herein is a userequipment (UE), in which at least one serving cell is set, fortransmitting power headroom (PH) information in a wireless communicationsystem, including a processor for generating the power headroominformation, and a transmission module for transmitting the powerheadroom information to a base station.

Alternatively or additionally, the power headroom information includes afirst field including a plurality of indicators and at least one secondfield indicating a level of the power headroom, and each of theplurality of indicators indicates whether the at least one second fieldexists for each of the at least one serving cell.

Alternatively or additionally, each of the plurality of indicators isset to 0 or 1, an indicator, which has been set to 1, indicates that asecond field exists for a corresponding serving cell, and an indicator,which has been set to 0, indicates that a second field does not existfor a corresponding serving cell.

Alternatively or additionally, the at least one second field may be foran activated serving cell among the at least one serving cell.

Alternatively or additionally, in the case in which generation of asecond field corresponding to any one of the at least one serving cellis triggered, the at least one second field may be for the whole of theat least one serving cell.

Alternatively or additionally, the power headroom information may betransmitted through one of the at least one serving cell.

Alternatively or additionally, the first field is a field in a bitmapform, and may be included the power headroom information regardless ofwhether the at least one second field exists.

According to embodiments of the present invention, a terminal caneffectively transmit power headroom information to a base station.

The effects of the present invention are not limited to the effectsmentioned above, and other effects will be clearly understood by thoseskilled in the art from the disclosure below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically showing a network structure of anE-UMTS as an exemplary radio communication system.

FIG. 2 is a diagram conceptually showing a network structure of anEvolved Universal Terrestrial Radio Access Network (E-UTRAN).

FIG. 3 is a diagram showing structures of a control plane and a userplane of a radio interface protocol between a UE and an E-UTRAN based onthe 3GPP radio access network specification.

FIG. 4 is a diagram showing physical channels used in a 3GPP system anda general signal transmission method using the same.

FIG. 5 is a diagram showing the structure of a radio frame used in anLTE system.

FIG. 6 is a diagram showing the concept of a carrier aggregation scheme.

FIG. 7 is a diagram showing the structure of power headroom informationdefined in an LTE system.

FIGS. 8A and 8B are diagrams showing the structure of an MAC subheaderdefined in an LTE system.

FIG. 9 is a diagram showing an MAC subheader and an MAC CE format forPHR-CA according to an exemplary embodiment of the present invention.

FIG. 10 is a diagram showing an MAC subheader and another MAC CE formatfor PHR-CA according to an exemplary embodiment of the presentinvention.

FIG. 11 is a block diagram of a communication device according to anexemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, structures, operations, and other features of the presentinvention will be understood readily from the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. Embodiments described later are examples in which technicalfeatures of the present invention are applied to a 3GPP system.

For convenience, although the embodiments of the present invention willbe described based on the LTE system and the LTE-A system, the LTEsystem and the LTE-A system are only exemplary and the embodiments ofthe present invention can be applied to all communication systemscorresponding to the aforementioned definition. Also, although theembodiments of the present invention will herein be described based onFDD mode, the FDD mode is only exemplary and the embodiments of thepresent invention can easily be applied to H-FDD mode or TDD mode.

FIG. 2 is a diagram conceptually showing a network structure of anEvolved Universal Terrestrial Radio Access Network (E-UTRAN). Inparticular, the E-UTRAN system is a system which has been evolved fromthe existing UTRAN system. The E-UTRAN comprises cells (eNBs or basestations), and the cells are connected through X2 interface. The cellsare connected with the user equipment (UE) through the wirelessinterface, and are connected with the evolved packet core (EPC) throughS1 interface.

The EPC comprises a mobility management entity (MME), a serving-gateway(S-GW) and a packet data network-gateway (PDN-GW). The MME hasconnection information of an UE or information on capability of the UE,and such information is mainly used for mobility management. The S-GW isa gateway having the E-UTRAN as the endpoint.

FIG. 3 is a diagram showing structures of a control plane and a userplane of a radio interface protocol between a UE and an E-UTRAN based onthe 3GPP radio access network specification. The control plane refers toa path used for transmitting control messages, which are used by a UserEquipment (UE) and a network to manage a call. The user plane refers toa path used for transmitting data generated in an application layer,e.g., voice data or Internet packet data.

A physical layer of a first layer provides an information transferservice to an upper layer using a physical channel. The physical layeris connected to a Medium Access Control (MAC) layer of an upper layervia a transport channel. Data is transported between the MAC layer andthe physical layer via the transport channel. Data is also transportedbetween a physical layer of a transmitting side and a physical layer ofa receiving side via a physical channel. The physical channel uses timeand frequency as radio resources. Specifically, the physical channel ismodulated using an Orthogonal Frequency Division Multiple Access (OFDMA)scheme in downlink and is modulated using a Single-Carrier FrequencyDivision Multiple Access (SC-FDMA) scheme in uplink.

A Medium Access Control (MAC) layer of a second layer provides a serviceto a Radio Link Control (RLC) layer of an upper layer via a logicalchannel. The RLC layer of the second layer supports reliable datatransmission. The function of the RLC layer may be implemented by afunctional block within the MAC. A Packet Data Convergence Protocol(PDCP) layer of the second layer performs a header compression functionto reduce unnecessary control information for efficient transmission ofan Internet Protocol (IP) packet such as an IPv4 or IPv6 packet in aradio interface having a relatively narrow bandwidth.

A Radio Resource Control (RRC) layer located at the bottommost portionof a third layer is defined only in the control plane. The RRC layercontrols logical channels, transport channels, and physical channels inrelation to configuration, re-configuration, and release of radiobearers. The radio bearer refers to a service provided by the secondlayer to transmit data between the UE and the network. To this end, theRRC layer of the UE and the RRC layer of the network exchange RRCmessages.

One cell of the eNB (base station) is set to use one of bandwidths suchas 1.25, 2.5, 5, 10, 15, and 20 MHz to provide a downlink or uplinktransmission service to UEs. Different cells may be set to providedifferent bandwidths.

Downlink transport channels for data transmission from the network tothe UE include a Broadcast Channel (BCH) for transmitting systeminformation, a Paging Channel (PCH) for transmitting paging messages,and a downlink Shared Channel (SCH) for transmitting user traffic orcontrol messages. Traffic or control messages of a downlink multicast orbroadcast service may be transmitted through the downlink SCH or may betransmitted through an additional downlink Multicast Channel (MCH).

Meanwhile, uplink transport channels for data transmission from the UEto the network include a Random Access Channel (RACH) for transmittinginitial control messages and an uplink SCH for transmitting user trafficor control messages. Logical channels, which are located at an upperlevel of the transport channels and are mapped to the transportchannels, include a Broadcast Control Channel (BCCH), a Paging ControlChannel (PCCH), a Common Control Channel (CCCH), a Multicast ControlChannel (MCCH), and a Multicast Traffic Channel (MTCH).

FIG. 4 is a diagram showing physical channels used in a 3GPP system anda general signal transmission method using the same.

A UE performs an initial cell search operation such as establishment ofsynchronization with an eNB when power is turned on or the UE enters anew cell (S401). The UE may receive a Primary Synchronization Channel(P-SCH) and a Secondary Synchronization Channel (S-SCH) from the eNB,establish synchronization with the eNB, and acquire information such asa cell identity (ID). Thereafter, the UE may receive a physicalbroadcast channel from the eNB to acquire broadcast information withinthe cell. Meanwhile, the UE may receive a Downlink Reference Signal (DLRS) in the initial cell search step to confirm a downlink channel state.

Upon completion of the initial cell search, the UE may receive aPhysical Downlink Control Channel (PDCCH) and a Physical Downlink SharedChannel (PDSCH) according to information included in the PDCCH toacquire more detailed system information (S402).

Meanwhile, if the UE initially accesses the eNB or if radio resourcesfor signal transmission are not present, the UE may perform a randomaccess procedure (S403 to S406) with respect to the eNB. To this end,the UE may transmit a specific sequence through a Physical Random AccessChannel (PRACH) as a preamble (S403), and receive a response message tothe preamble through the PDCCH and the PDSCH corresponding thereto(S404). In the case of a contention-based RACH, a contention resolutionprocedure may be additionally performed.

The UE which performs the above procedures may receive a PDCCH/PDSCH(S407) and transmit a Physical Uplink Shared Channel (PUSCH)/PhysicalUplink Control Channel (PUCCH) (S408) according to a generaluplink/downlink signal transmission procedure. In particular, the UEreceives the downlink control information (DCI) through the PDCCH. Here,the DCI includes control information such as resource allocationinformation on the UE, and the format is different depending on thepurpose of use.

Control information transmitted by the UE to the eNB through uplink orreceived by the UE from the eNB through downlink includes adownlink/uplink ACK/NACK signal, a Channel Quality Indicator (CQI), aPrecoding Matrix Index (PMI), a Rank Indicator (RI), and the like. Inthe case of the 3GPP LTE system, the UE may transmit the controlinformation such as CQI/PMI/RI through the PUSCH and/or the PUCCH.

FIG. 5 is a diagram showing the structure of a radio frame used in anLTE system.

Referring to FIG. 5, the radio frame has a length of 10 ms (327200 Ts)and includes 10 equal-sized subframes. Each of the subframes has alength of 1 ms and includes two slots. Each of the slots has a length of0.5 ms (15360 Ts). In this case, Ts denotes sampling time and isrepresented by Ts=1/(15 kHz×2048)=3.2552×10-8 (about 33 ns). Each slotincludes a plurality of OFDM symbols in a time domain and includes aplurality of resource blocks in a frequency domain. In the LTE system,one resource block includes 12 subcarriers×7 (or 6) OFDM symbols. ATransmission Time Interval (TTI) which is a unit time for datatransmission may be determined in units of one or more subframes. Theabove-described structure of the radio frame is purely exemplary andvarious modifications may be made in the number of subframes included ina radio frame, the number of slots included in a subframe, or the numberof OFDM symbols included in a slot.

Hereinafter, an RRC state of the UE and a method of connecting RRC willnow be described in detail. The RRC state refers to whether or not theRRC of a user equipment (UE) is in a logical connection with the RRC ofa E-UTRAN. In case the RRCs are logically connected to one another, theRRC state is indicated as an RRC_CONNECTED state. And, in case the RRCsare not logically connected to one another, the RRC state is indicatedas RRC_IDLE state.

Since an RRC connection exists in the UE of the RRC_CONNECTED state, theE-UTRAN may recognize the existence of the corresponding user equipment(UE) in the cell unit and may effectively control the user equipment(UE). Conversely, the E-UTRAN is incapable of recognizing the UE of theRRC_IDLE state. And, herein, an EPC manages the UE in Tracking Areaunits, which correspond to area units larger than the cell units. Thatis, in order to receive generic mobile communication services, such assound (or audio data) or data, the RRC should be shifted to theRRC_CONNECTED state.

When the user initially turns on the power of the UE, the UE searchesfor an adequate cell and remains in the RRC_IDLE state within thecorresponding cell. Once the UE that was in the RRC Idle state isrequired to make an RRC connection, the RRC of the UE can then make anRRC connection with the RRC of the E-UTRAN through an RRC connectionestablishment procedure, thereby shifting to the RRC_CONNECTED state.Examples of when the UE, which was in the RRC_IDLE state, is required tomake an RRC connection includes a case when an uplink data transmissionis required due to reasons, such as the user's attempt to make a phonecall, or a case when a response message transmission is required to bemade after receiving a paging message from the E-UTRAN.

FIG. 6 is a conceptual diagram illustrating a carrier aggregationscheme. Carrier aggregation refers to a method of using a plurality offrequency blocks or cells composed of uplink resources (or componentcarriers) and/or uplink resources (or component carriers) as a largelogical frequency band in order to use a wider frequency band in a radiocommunication system. Hereinafter, for the convenience of explanation,the component carriers are expressed as serving cells.

Referring to FIG. 6, an entire system band is a logical band having amaximum bandwidth of 100 MHz. The entire system band includes fiveserving cells (SC) and each SC has a maximum bandwidth of 20 MHz. The SCincludes one or more physically contiguous subcarriers. Although all SCshave the same bandwidth in FIG. 6, this is only exemplary and the SCsmay have different bandwidths. Although the SCs are shown as beingcontiguous in the frequency domain in FIG. 6, FIG. 6 merely shows thelogical concept and thus the SCs may be physically contiguous orseparated.

Different center frequencies may be used for the SCs or one commoncenter frequency may be used for physically contiguous SCs. For example,in FIG. 10, if it is assumed that all SCs are physically contiguous, acenter frequency A may be used. If it is assumed that SCs are notphysically contiguous, a center frequency A, a center frequency B andthe like may be used for the respective SCs.

In the present specification, the SC may correspond to a system band ofa legacy system. By defining the SC based on the legacy system, it ispossible to facilitate backward compatibility and system design in aradio communication environment in which an evolved UE and a legacy UEcoexist. For example, if the LTE-A system supports carrier aggregation,each SC may correspond to the system band of the LTE system. In thiscase, the SC may have any one bandwidth such as 1.25, 2.5, 5, 10 or 20MHz.

In the case in which the entire system band is extended by carrieraggregation, a frequency band used for communication with each UE isdefined in SC units. A UE A may use 100 MHz which is the bandwidth ofthe entire system band and perform communication using all five SCs.Each of UEs B1 to B5 may only use a bandwidth of 20 MHz and performcommunication using one SC. Each of UEs C1 and C2 may use a bandwidth of40 MHz and perform communication using two SCs. The two SCs may belogically/physically contiguous or discontiguous. The UE C1 uses twodiscontiguous SCs and the UE C2 uses two contiguous SCs.

The LTE-A system suggests a concept of calling a serving cell, in whichall control signals are transmitted, a primary serving cell. An uplinkprimary serving cell and a downlink primary serving cell may be includedin each UE, and such a combination of the uplink primary serving cell,which is used in transmission of uplink control information, and thedownlink primary serving cell, which is used in transmission of downlinkcontrol information, may be called a primary cell or a PCell. The cellsincluded in the UE other than the primary cell or PCell may be called asecondary cell or a SCell.

Further, in order for a UE to transmit data to the base station,transmission power should be appropriately regulated. In the case inwhich the transmission power of the UE is too low, there is a highprobability that the base station does not receive data transmitted bythe UE. Further, in the case in which the transmission power is toohigh, the base station may receive the data of the UE, but it may bedifficult to receive the data transmitted by a UE other than the UE.

Therefore, in order to prevent performance deterioration of thetransmission and reception of the data of the entire LTE system, thebase station needs to optimize the transmission power of the UE.

In order for the base station to adjust the transmission power of theUE, the base station should obtain information for control of thetransmission power from the UE. A power headroom report (PHR) of the UEis used for this, and here, the power headroom refers to power which maybe additionally used in addition to the power currently transmitted bythe UE. In other words, the power headroom refers to the differencebetween the maximum power, which may be transmitted by the UE, and thepower, which is currently being transmitted by the UE.

If the base station receives a report on the power headroom from the UE,the base station determines power to be used in the next uplinktransmission of the UE on the basis of the received power headroominformation.

Such determined transmission power is expressed as the size of theresource block and the modulation and coding scheme (MCS), and istransmitted to the UE when allocating the uplink (UL) grant of the nexttransmission period.

At this time, transmitting, by the UE, the power headroom report toofrequently may cause deterioration of the performance by causing a wasteof wireless resources. Hence, the UE may configure the power headroomreport only in the case in which preset conditions are satisfied.Hereinafter, this is called a PHR trigger condition.

The PHR trigger condition may include the conditions described below.First, after transmitting the power headroom report to the base station,the case, in which the path loss exceeds a preset range, may be set as acondition. Next, the case, which a parameter related with the powerheadroom information is set or reset, or the case, in which a presetpower headroom information timer expires, may be set as a condition.However, the above described conditions are merely exemplary, and it ispossible to set various conditions as a PHR trigger condition withoutany limitation.

In the case in which a preset condition is satisfied, the configurationof the power headroom report of the UE is triggered, and if there is anewly received uplink (UL) grant in the TTI, the UE performstransmission of the power headroom report through the process describedbelow.

That is, the UE receives the power headroom information level valuetransmitted from the physical layer, and generates and transmits the PHRMAC control element (CE) on the basis of the power headroom informationlevel value. Thereafter, the UE may restart the preset power headroominformation timer.

As described, above, when transmitting the power headroom information,the UE transmits the information in the form of a PHR MAC CE, and thiswill be described below in more detail.

FIG. 7 is a diagram showing the structure of power headroom informationdefined in an LTE system.

In FIG. 7, the power headroom information includes a reserved bit and aPH field. The portion expressed as R is the reserved bit, and the actualpower headroom value is reported through the PH field. In the currentLTE system, 6 bits are used in the PH field, and a total of 64 powerheadroom information level values may be notified.

In order for the UE to transmit the power headroom information throughthe PHR MAC CE, the logical channel ID (LCID) value for the PHR MAC CEis allocated in the uplink shared channel (UL-SCH) (e.g., the ID valueof 11010 is allocated as the LCID). This will be described in moretailed with reference to FIGS. 8A and 8B.

FIGS. 8A and 8B are diagrams showing the structure of a MAC subheaderdefined in an LTE system.

In particular, FIG. 8A illustrates the structure of a subheader ofR/R/E/LCID type.

Referring to FIG. 8A, R is a reserved bit, and is set to 0. Further, Eis an extension field, and includes a flag bit indicating whether thereis an additional field in the MAC header. That is, in the case in whichE is set to 1, it is indicated that there is another header ofR/R/E/LCID type.

Lastly, the LCID is a logical channel identifier field, and indicateswhether there is a corresponding local channel or MAC CE. For example,in the existing LTE system, in the case in which the LCID is set to11010, it is indicated that there is an MAC CE including a PHR.

Therefore, the effect of indicating the existence of the MAC CEincluding the power headroom information in advance through the LCID isguaranteed.

Based thereon, as shown in FIG. 8B, a PDU including the MAC header, MACCE, MAC SDU and padding bit, etc., may be transmitted.

Further, in the LTE-A system, as the carrier aggregation technology isintroduced, there came to be a need for a change in the power headroomreport (PHR).

The PHR of the existing LTE system reported the power headroom for onecell, but if the carrier aggregation technology is introduced, aplurality of serving cells are used, and thus the power headroom for theplurality of serving cells needs to be reported.

Therefore, a new PHR format and operation method for the carrieraggregation technology should be designed.

The present invention provides a method for reporting, by an UE, thepower headroom for a plurality of serving cells using a new PHR format.

Here, it may not be necessary to report the power headroom for all ofthe plurality of serving cells which have been set in the UE. Forexample, if a certain serving cell is set, the cell may be in anactivated or deactivated state depending on the state, the serving cellin the deactivated state does not need to report the power headroombecause the cell is not used until the cell is activated. Therefore, theUE may need to transmit only the power headroom information on at leastone activated serving cell.

To this end, the power headroom information including a plurality ofpower headroom reports may indicate whether there is a power headroomlevel for each of the plurality of serving cells by having a fieldincluding a plurality of indicators. That is, the UE generates powerheadroom information, which includes at least one first field includinga plurality of indicators and a plurality of second fields indicatingrespective power headroom levels of serving cells, and transmits thegenerated power headroom information to the base station.

Hereinafter, for the convenience of explanation, a field including aplurality of indicators is called a first field, and a field, whichindicates the power headroom level for each serving cell, is called asecond field.

As described above, since a second field indicates the power headroomlevel for at least one serving cell, the field may be singular orplural, and each of the plurality of indicators included in the firstfield indicates whether the second field exists for each of the at leastone serving cell.

Preferably, each of the plurality of indicators may be set to 0 or 1. Atthis time, the indicator, which has been set to 1, may indicate thatthere is a second field for the corresponding serving cell, and theindicator, which has been set to 0, may indicate that there is not asecond field for the corresponding serving cell.

Here, the first field is a field of a bitmap form, may be included inthe power headroom information regardless of whether there is at leastone second field, and may be transmitted.

Further, a subheader, which includes an LCID that is used to notify theexistence of the power headroom information including a plurality ofpower headroom reports, may be transmitted along with the power headroominformation. Hence, the effect of easily recognizing the existence ofthe power headroom information including a plurality of power headroomreports through a newly designated LCID is guaranteed.

Further, in the case in which the UE receives the setting of a pluralityof serving cells from the base station (eNB), each of the serving cellsis given a cell index for mutual identification, and the first field andthe second field may be included in the power headroom informationaccording to each cell index.

The number of serving cells, which may be actually operable in thecarrier aggregation technology, is 5, and the cell index is allocatedbetween 0 and 4.

For example, the second field may be included in the power headroominformation from the smallest cell index of each corresponding cell tothe largest cell index in order. In response thereto, each of theplurality of indicators included in the first field may be sequentiallyarranged in the first field from the right to the left according to thecell index of a corresponding cell.

At this time, transmitting, by the UE, the power headroom report on theplurality of serving cells too frequently may cause deterioration ofperformance by causing a waste in radio resources by the transmissionitself. Hence, the UE may constitute the power headroom report on theplurality of serving cells only in the case in which a preset conditionis satisfied. Hereinafter, the condition is called a PHR-CA triggercondition.

The PHR-CA trigger condition may include the conditions below. First,after the power headroom report is transmitted to the base station(eNB), a case in which the path loss exceeds a preset range may be setas a condition. Next, a case in which the parameter related with thepower headroom information is set or reset, or a case in which a presetpower headroom information timer expires, etc. may be set as acondition. However, the above listed conditions are merely examples, andvarious conditions may be set as a PHR-CA trigger condition without anylimitation.

In the case in which any one of the plurality of serving cells satisfiesthe above condition, the configuration of the power headroom report ofthe UE is triggered, and in the case in which there is a newly receivedUL grant in the TTI, the transmission of the power headroom report onthe plurality of serving cells is performed through the processdescribed below.

That the UE receives the power headroom information level valuetransmitted from the physical layer, generates the PHR MAC controlelement (CE) based on the power headroom information level value, andtransmits the generated PHR MAC control element. Thereafter, the UE mayrestart the preset power headroom information timer.

At this time, although a plurality of serving cells have been set in theUE, the power headroom information may be transmitted only through oneserving cell.

Further, in the case in which the generation of the second field on oneserving cell among a plurality of serving cells is triggered, thegeneration of the second field on the whole of at least one serving cellmay be triggered.

More details of the present invention will be described with referenceto drawings.

FIG. 9 is a diagram showing an MAC subheader and an MAC CE format forPHR-CA according to an exemplary embodiment of the present invention.

First, referring to FIG. 9, R included in the MAC subheader is areserved field and is set to 0, and E is an extension field and notifieswhether there is an additional MAC subheader in the next. The logicalchannel ID (LCID) field gives information on which content is includedin the MAC CE, and a new value is used in the LCID to notify that theMAC CE is a newly defined PHR-CA MAC CE.

Next, the PHR-CA MAC CE indicates information on the serving cell, forwhich the PHR-CA MAC CE includes the PHR, including the first fieldcomposed of a plurality of indicators in the first byte.

In the carrier aggregation technology, since a maximum of five servingcells may be used, the first field of 5 bits may be used, and the cellindex of each serving cell is one to one mapped to each of theindicators of the first field.

The second field for each serving cell is included only when theindicator of the first field is set to 1. That is, the UE configures thePHR-CA including the second field only for the serving cell which needsreporting.

In FIG. 9, indicators corresponding to the small cell index are arrangedfrom the rightmost to the left. Further, the second field for eachserving cell is included in the power headroom information in anascending order from the small cell index.

Therefore, referring to the first field, only the indicatorscorresponding to serving cells 1 and 4 have been set to 1, and thus onlythe second field corresponding to serving cells 1 and 4 is included inthe power headroom information.

Further, in the PHR-CA MAC CE format, 8 bits, not 5 bits, may be usedfor the first field according to the range of the cell index. That is,when a cell index of three bits is used, the range of the index isbetween 0 and 7, and in this case, the first field should also use 8bits. However, even if the range of the cell index is 0 to 7, the numberof serving cells, which are actually set, may be equal to or less than5.

Here, the serving cell, whose cell index is 0, is a primary cell, andmay include two types of PHRs. First, PHR type 1, which is a differencebetween the maximum power that may be transmitted through the primarycell, and the power that is transmitted in the current physical uplinkshared channel (PUSCH), may be included. Further, PHR type 2, which is adifference between the maximum power that may be transmitted through theprimary cell, and the power that is transmitted in the current physicaluplink shared channel (PUSCH) and physical uplink control channel(PUCCH), may be included.

The first field of 8 bits, PHR type 1 and PHR type 2 will bespecifically described with reference to drawings.

FIG. 10 is a diagram showing an MAC subheader and another MAC CE formatfor PHR-CA according to an exemplary embodiment of the presentinvention.

The first field of 8 bits is used in FIG. 10. As in FIG. 9, indicatorscorresponding to the small cell index are arranged from the rightmost tothe left, and the second field for each serving cell is included in thepower headroom information in an ascending order from the small cellindex. Further, the second field for each serving cell is included onlywhen the indicator of the first field is set to 1.

Referring to the first field, only the indicators corresponding toserving cells 1, 4 and 6 have been set to 1, and thus only the secondfield corresponding to serving cells 1, 4 and 6 are included in thepower headroom information.

At this time, serving cell 1 is a primary cell, and may have the secondfield of PHR type 1 and PHR type 2.

Hence, the final power headroom information includes PHR type 1 and PHRtype 2 of serving cell 1, PHR of serving cell 4 and PHR of serving cell6.

FIG. 11 is a block diagram of a communication device according to anexemplary embodiment of the present invention.

Referring to FIG. 11, the communication device 1100 includes a processor1110, a memory 1120, an RF module 1130, a display module 1140, and auser interface module 1150.

The communication device 1100 has been illustrated for the convenienceof explanation, and some modules may be omitted. Further, thecommunication device 1100 may further include necessary modules.Further, some modules may be divided into more specific modules in thecommunication device 1100. The processor 1110 may be configured toperform operation according to an exemplary embodiment of the presentinvention with reference to drawings. Specifically, the specificoperation of the processor 1110 has been described above with referenceto FIGS. 1 to 10.

The memory 1120 is connected with the processor 1110 and stores anoperating system, an application, a program code, and data therein. TheRF module 1130 is connected with the processor 1110 and converts abaseband signal to a radio signal or vice versa. To this end, the RFmodule 1130 performs analog conversion, amplification, filtering andfrequency uplink conversion, or their reverse processes. The displaymodule 1140 is connected with the processor 1110 and displays variouskinds of information. Examples of the display module 1140 include, butnot limited to, a liquid crystal display (LCD), a light emitting diode(LED), and an organic light emitting diode (OLED). The user interfacemodule 1150 is connected with the processor 1110, and may be configuredby combination of well known user interfaces such as keypad and touchscreen.

The aforementioned embodiments are achieved by combination of structuralelements and features of the present invention in a predetermined type.Each of the structural elements or features should be consideredselectively unless specified separately. Each of the structural elementsor features may be carried out without being combined with otherstructural elements or features. Also, some structural elements and/orfeatures may be combined with one another to constitute the embodimentsof the present invention. The order of operations described in theembodiments of the present invention may be changed. Some structuralelements or features of one embodiment may be included in anotherembodiment, or may be replaced with corresponding structural elements orfeatures of another embodiment. Moreover, it will be apparent that someclaims referring to specific claims may be combined with another claimsreferring to the other claims other than the specific claims toconstitute the embodiment or add new claims by means of amendment afterthe application is filed.

The embodiments of the present invention have been described based onthe data transmission and reception between the base station and theuser equipment. A specific operation which has been described as beingperformed by the base station may be performed by an upper node of thebase station as the case may be. In other words, it will be apparentthat various operations performed for communication with the userequipment in the network which includes a plurality of network nodesalong with the base station can be performed by the base station ornetwork nodes other than the base station. The base station may bereplaced with terms such as a fixed station, Node B, eNode B (eNB), andaccess point.

The embodiments according to the present invention may be implemented byvarious means, for example, hardware, firmware, software, or theircombination. If the embodiment according to the present invention isimplemented by hardware, the embodiment of the present invention may beimplemented by one or more application specific integrated circuits(ASICs), digital signal processors (DSPs), digital signal processingdevices (DSPDs), programmable logic devices (PLDs), field programmablegate arrays (FPGAs), processors, controllers, microcontrollers,microprocessors, etc.

If the embodiment according to the present invention is implemented byfirmware or software, the embodiment of the present invention may beimplemented by a type of a module, a procedure, or a function, whichperforms functions or operations described as above. A software code maybe stored in a memory unit and then may be driven by a processor. Thememory unit may be located inside or outside the processor to transmitand receive data to and from the processor through various means whichare well known.

It will be apparent to those skilled in the art that the presentinvention can be embodied in other specific forms without departing fromthe spirit and essential characteristics of the invention. Thus, theabove embodiments are to be considered in all respects as illustrativeand not restrictive. The scope of the invention should be determined byreasonable interpretation of the appended claims and all change whichcomes within the equivalent scope of the invention are included in thescope of the invention.

The method for allowing a terminal to transmit power headroominformation in a wireless communication system, and an apparatus for thesame have been described based on an example applicable to 3GPP LTEsystem, but may be applicable to various wireless communication systemsother than the 3GPP LTE system.

What is claimed is:
 1. A method for transmitting, by a user equipment(UE) with which a primary cell and at least one secondary cell areconfigured, power headroom (PH) information in a wireless communicationsystem, the method comprising: generating the PH information; andtransmitting the PH information to a base station, wherein the PHinformation includes a first field including a plurality of indicators,each of the plurality of indicators indicating the presence of a secondfield indicating a PH level of a corresponding secondary cell, andwherein the PH information further includes a type-1 PH field and atype-2 PH field for only the primary cell.
 2. The method according toclaim 1, wherein each of the plurality of indicators is set to 0 or 1,wherein an indicator, which has been set to 1, indicates that the secondfield exists for the corresponding secondary cell, and wherein anindicator, which has been set to 0, indicates that the second field doesnot exist for the corresponding secondary cell.
 3. The method accordingto claim 1, wherein the second field is for an activated secondary cell.4. The method according to claim 1, wherein when generation of thesecond field is triggered, the second field is for all of the at leastone secondary cell.
 5. The method according to claim 1, wherein the PHinformation is transmitted through one of the primary component carrierand the at least one secondary cell.
 6. The method according to claim 1,wherein the first field is a field in a bitmap form, and is included inthe PH information regardless of whether the second field exists.
 7. Themethod according to claim 1, wherein the PH information is included in amedium access control (MAC) control element (CE), and is transmitted. 8.The method according to claim 7, wherein the MAC CE further includes alogical channel ID (LCID) for notifying existence of the PH information.9. The method according to claim 1, wherein the second field isconfigured in a cell index order of the at least one secondary cell. 10.The method according to claim 1, wherein the type-1 PH field indicatesthe PH level calculated based on transmission power of a physical uplinkshared channel (PUSCH) transmitted through the primary cell.
 11. Themethod according to claim 10, wherein the PH level indicated by thetype-1 PH field is determined based on a difference between maximumtransmission power for the primary cell and current transmission powerof the PUSCH.
 12. The method according to claim 1, wherein the type-2 PHfield indicates the PH level calculated based on transmission power of aphysical uplink shared channel (PUSCH) and a physical uplink controlchannel (PUCCH) transmitted through the primary cell.
 13. The methodaccording to claim 12, wherein the PH level indicated by the type-2 PHfield is determined based on a difference between maximum transmissionpower for the primary cell and current transmission power of the PUSCHand the PUCCH.
 14. A user equipment (UE) with which a primary cell andat least one secondary cell are configured, for transmitting powerheadroom (PH) information in a wireless communication system, the UEcomprising: a processor configured to generate the PH information; and atransmitter configured to transmit the PH information to a base station,wherein the PH information includes a first field including a pluralityof indicators, each of the plurality of indicators indicating thepresence of a second field indicating a PH level of a correspondingsecondary cell, and wherein the PH information further includes a type-1PH field and a type-2 PH field for only the primary cell.
 15. The UEaccording to claim 14, wherein each of the plurality of indicators isset to 0 or 1, wherein an indicator, which has been set to 1, indicatesthat the second field exists for the corresponding secondary cell, andwherein an indicator, which has been set to 0, indicates that the secondfield does not exist for the corresponding secondary cell.
 16. The UEaccording to claim 14, wherein the second field is for an activatedsecondary cell.
 17. The UE according to claim 14, wherein whengeneration of the second field is triggered, the second field is for allof the at least one secondary cell.
 18. The UE according to claim 14,wherein the PH information is transmitted through one of the primarycell and the at least one secondary cell.
 19. The UE according to claim14, wherein the first field is a field in a bitmap form, and is includedin the PH information regardless of whether the second field exists. 20.The UE according to claim 14, wherein the PH information is included ina medium access control (MAC) control element (CE), and is transmitted.21. The UE according to claim 20, wherein the MAC CE further includes alogical channel ID (LCID) for notifying existence of the PH information.22. The UE according to claim 14, wherein the second field is configuredin a cell index order of the at least one secondary cell.
 23. The UEaccording to claim 14, wherein the type-1 PH field indicates the PHlevel calculated based on transmission power of a physical uplink sharedchannel (PUSCH) transmitted through the primary cell.
 24. The UEaccording to claim 23, wherein the PH level indicated by the type-1 PHfield is determined based on a difference between maximum transmissionpower for the primary cell and current transmission power of the PUSCH.25. The UE according to claim 14, wherein the type-2-PH field indicatesthe PH level calculated based on transmission power of a physical uplinkshared channel (PUSCH) and a physical uplink control channel (PUCCH)transmitted through the primary cell.
 26. The UE according to claim 25,wherein the PH level indicated by the type-2 PH field is determinedbased on a difference between maximum transmission power for the primarycell and current transmission power of the PUSCH and the PUCCH.
 27. Abase station (BS) for receiving power headroom (PH) information in awireless communication system, the BS comprising: a transceiverconfigured to transmit and receive a radio signal; and a processor,wherein the processor is configured to control the transceiver toreceive the PH information from a user equipment (UE) with which aprimary cell and at least one secondary cell are configured, wherein thePH information includes a first field including a plurality ofindicators, each of the plurality of indicators indicating the presenceof a second field indicating a PH level of a corresponding secondarycell, and wherein the PH information further includes a type-1 PH fieldand a type-2 PH field for only the primary cell.